Recent years have seen widespread use of multiphase power supply equipment consisting of a plurality of switching power supply devices connected in parallel so as to be driven out of phase from one another. Power supply equipment of such a configuration is advantageously capable of outputting high current in proportion to the number of phases, i.e., the number of switching converters used.
As a switching power supply device used in multiphase power supply equipment, for example, a switching power supply device 100 shown in FIG. 11 is known (see, for example, Non-Patent Document 1). In the switching power supply device 100, as shown in the figure, a converter portion 2, which is a step-down DC-DC converter, steps down an input voltage Vi outputted by a direct-current power supply 30 and outputs an output voltage vo, which is equal to a preset target voltage Vr, to a load 31, and in addition to the converter portion 2, the switching power supply device 100 includes a pulse width modulation circuit 101 for generating a square-wave voltage VPWM to drive switching elements included in the converter portion 2.
The pulse width modulation circuit 101 includes an error amplifier portion 102 for outputting an error voltage vc between the output voltage vo and the target voltage Vr, a comparator portion 103 provided with a comparator 16 having a positive input terminal to which the error voltage vc is inputted via a first resistor 15 and a negative input terminal to which an integrated voltage vn, which is obtained by integrating a square-wave voltage VPWM outputted from an output terminal, is inputted, the output terminal being connected to the positive input terminal via a second resistor 17, and a clock portion 104 for applying a clock signal VCL to the positive input terminal of the comparator 16.
In the switching power supply device 100, when the voltage vp at the positive input terminal is lower than the integrated voltage vn, the voltage vp at the positive input terminal is forcibly raised to H level in accordance with a change of the clock signal VCL, as shown in FIGS. 12(A) and 12(B). That is, in the switching power supply device 100, the square-wave voltage VPWM changes in synchronization with the clock signal VCL.
In general, self-oscillating switching power supply devices have an issue in that due to operating frequency fluctuations in accordance with load fluctuations, there is difficulty in phase synchronization in a multiphase configuration achieved by connecting a plurality of switching power supply devices in parallel. In this regard, in the case of the switching power supply device 100, this issue can be solved by inputting the same clock signal VCL to each of the phases, i.e., the switching power supply devices 100 connected in parallel.